1. Technical Field of the Invention
This invention relates to computer input devices, and more particularly, to a keyboard which produces little or no impact on a user""s fingers, thereby decreasing the risk of a repetitive stress injury such as carpal tunnel syndrome.
2. Description of Related Art
Along with the rapid growth of machine automation and the widespread personal and professional use of computers, there has been an increase in repetitive stress injuries. Commonly occurring in the workplace, these injuries include upper limb disorders such as xe2x80x9cCarpal Tunnel Syndromexe2x80x9d, cumulative trauma disorder, and occupational overuse syndrome.
Frequent users of personal computers, such as shown in FIG. 1, are at risk for a repetitive stress injury when interacting with the device through a standard electronic keyboard. Stress injuries arise from accumulative strain on the limbs over a period of time. In contrast to using a traditional manual typewriter, the computer keyboard user no longer takes breaks from data input for carriage returns, error corrections, and paper insertions. Instead, the user achieves the equivalent of these functions with additional keystrokes, never removing the hands from the keyboard or repositioning the arms to reach for items such as correction fluid, paper, or an adding machine.
This uninterrupted use places a continuous strain on the fingers and upper limbs, especially due to the stress of the constant impact from the keyboard. When each key reaches the bottom of a keystroke, it xe2x80x9cbottoms out,xe2x80x9d causing a small impact to the fingers as the key hits onto a hard plastic surface or non-resilient material. The vibration of impact travels up the hand and arm, stressing the soft tissues such as the muscles, tendons, and ligaments. This is similar to the vibration of impact traveling up the leg of a runner when his foot hits the ground, causing his muscles and joints to become sore. Typing on a keyboard without any cushion for the impact of the keys is similar to a person running without cushioning in his shoes, quickly leading to soreness and pain if done continuously, and contributing to the development of a repetitive stress injury.
For example, with reference to FIG. 1, a personal computer system typically includes a computer 12, a display device 14, a keyboard 15 and a mouse 16. The standard keyboard 16 includes an alphanumeric keypad 18, a row of function keys 20, a numeric keypad 22 and a command keypad 24. While seated at the computer system 10, facing the display 14, the user""s upper torso, arms, wrists, and hands rarely change position while the user""s fingers are operating the keyboard 15. This uninterrupted, repetitive impact of the fingers over a standard keyboard may cause excessive use and chronic fatigue of the muscles and tendons, causing the tendons to swell, and at the same time, squeezing the median nerve as it passes through the wrist ligament. This leads to pain and discomfort, and it is commonly associated with symptoms such as numbness, burning, and tingling sensations in the hands and arms. These symptoms are commonly associated with Carpal Tunnel Syndrome, a syndrome of median nerve compression with symptoms in the hands and arm where the nerve runs. Medical treatments for this condition include physical therapy and surgery to relieve the pressure on the median nerve.
FIGS. 2-4 illustrate the tissue and nerves affected by carpal tunnel syndrome, depicting the human wrist 30 in FIGS. 2 and 3, and the arm 40 in FIG. 4. With reference to FIGS. 2-4, carpal tunnel syndrome is caused by compression of the median nerve 31, which travels from the neck to the fingers, through the upper arm 22, forearm 24, wrist 25, and hand 28. The palmar carpal ligament 32, shown reflected in FIG. 2, wraps around the bones 27, 29, of the wrist 25, otherwise known as the carpals, to form the carpal tunnel 35. The muscles 23 of the forearm 24 are attached by the tendons 26 to the fingers and travel underneath the carpal ligament 32, as does the median nerve 31.
Carpal tunnel syndrome occurs when the tissues in the carpal tunnel 35 become irritated and as a result, swell and eventually compress the median nerve 31, causing the symptoms noted above. Traditional writings on carpal tunnel syndrome have identified the cause of the irritation and swelling variously as chronic fatigue of the muscles, overuse of the tendons, and rubbing of the tendons, muscles and bones due to repetitive use of the hands and fingers. In particular, holding the wrists in xe2x80x9cunnaturalxe2x80x9d positions enhance the rubbing of tendons and contribute to muscle fatigue. For example, the position of the wrist while typing on a conventional, straight keyboard has been cited as a major contributor to carpal tunnel syndrome.
As a result of the above diagnosis of the cause of carpal tunnel syndrome, the prior art approaches to preventing these injuries include adjusting the work environment to better fit the user""s body. These ergonomic adjustments include the use of wrist pads, split keyboards, keyboard replacements, and keyboards and drawers with wrist supports unitarily formed within. Devices such as the split keyboard create a xe2x80x9cnaturalxe2x80x9d position of the user""s wrists while typing. These devices, however, have not significantly reduced the incidence of carpal tunnel syndrome.
The Applicant""s research suggests that the traditional view of the cause of carpal tunnel syndrome is limited, and as a result, the prior art solutions to the problem have been largely ineffective. Carpal tunnel syndrome does not occur merely from repetitively using the fingers and hands. For thousands of years, people have worked at repetitive upper limb tasks which have not led to the large numbers of persons experiencing the symptoms described above. Even with the advent of the manual typewriter, there were not reported cases of symptoms similar to carpal tunnel syndrome.
Instead, the cause of the tissue irritation is from the loading placed on the muscles and tendons of the arm, and the repetitive impact stress caused by typing on keyboards on which the keys strike a hard surface at the bottom of the keystroke. The use of the non-giving design of a traditional keyboard is similar to repetitively striking the fingers against a hard desk top, or like a person running on hard concrete without cushioned shoes. The harder the fingers are struck, the more evident the xe2x80x9cbone jarringxe2x80x9d impact becomes. Each impact causes tension in the tendons to spike to high levels, and sets up a vibration which must be absorbed by the surrounding tissues. Although the impact of fingers on a keyboard may not appear injurious, research shows that the loading on the muscles is much higher than expected, and the repetitive impact and resultant vibrations from thousands of keystrokes that end on a hard solid surface causes the tissues in the carpal tunnel 35 to become irritated, and as a result, to swell and eventually compress the median nerve 31.
The prior art neither teaches nor suggests a means to lessen the strain placed on the upper limbs through repetitive absorption of vibrations from the impact of each keystroke. In order to decrease the risk of a repetitive stress injury, it would be advantageous to have a no-impact keyboard which reduces or eliminates the vibrations and tissue irritations associated with the repetitive impact of the fingers. The present invention provides such a solution.
The present invention provides an improved keyboard for decreasing the risk of repetitive stress injuries. The no-impact keyboard of the invention incorporates a means for cushioning each keystroke to decrease or eliminate the vibrational impact traditionally absorbed into the body when the key reaches the hard bottom of the keystroke.
According to a preferred embodiment, the no-impact keyboard includes a plurality of keys, each of the keys comprising a key cap and a stem; an impact absorbing mechanism which prevents any part of a key from striking a hard surface during a keystroke by a typist""s finger; and means for sending an actuation signal from each key when the key passes a defined point in the keystroke.
In another aspect, the present invention is an impact absorbing keyboard comprising a plurality of keys, each of the keys having a cap and a stem with a bottom end; a circuit board mounted under the plurality of keys; means for each key to make electrical contact with the circuit board; and an impact absorbing spring having a spring tension sufficient to prevent the bottom end of the stem from striking the circuit board when the key cap is struck.